Influence of Temperature on the Sorption of Humic Substances on Ferrihydrite-Coated Quartz Under Dynamic Flow Conditions.

Understanding the processes that govern natural organic matter (NOM) stabilization and degradation are crucial for accurate modeling of carbon cycling and for predicting the impacts of climate change. Sorption to mineral surfaces has been implicated as a chief mechanism for long-term preservation of NOM. Iron, the fourth most abundant element in the earth’s crust, creates oxide minerals and surface coatings that act as effective sorbents of NOM. The extent and strength of these interactions depend on pH, temperature, ionic strength, soil moisture, and NOM molecular composition.

            In this study, we assessed the impact of temperature on the sorption and desorption behavior of Suwannee River natural organic matter (NOM), fulvic acid (FA), and humic acid (HA) and Elliott soil humic acid within packed columns of ferrihydrite-coated sand at neutral pH. At 25˚C, the HA solutions broke through their respective columns faster than the FA and NOM solutions, meaning more FA and NOM sorbed to the ferrihydrite-coated sand. Immediately following breakthrough, the concentrations of organic matter (OM) in the effluent solutions increased rapidly for several pore volumes, then gradually slowed as the OM concentrations approached the initial concentrations. At 25˚C, the HA also desorbed more rapidly and to a greater extent than the FA and NOM. The adsorption of HA was positively correlated with increasing temperature while adsorption of FA was not found to be temperature sensitive. Some key compositional differences between the HA and FA fractions may explain these differences in behavior: Suwannee River FA contains more aliphatic carbon and carboxylic acids while Suwannee River HA and Elliott Soil HA contain more carbohydrates, aromatic carbon, and amino acids. These results indicate that increasing soil temperature may reduce the amount of bioavailable HA in iron rich environments but have little influence on the more strongly sorbing FA.